OPTICAL MODULATOR
An optical modulator is disclosed, in which a MMI couplers are used for input signal splitting for branching into individual Mach-Zehnder interferometers, as well as for branching and combining from individual Mach-Zehnder waveguides. MMI couplers, splitters, and combiners may be cascaded and combined with single-mode Y-splitters and combiners to provide modulators of various types, including dual polarization, quadrature phase Mach-Zehnder interferometer base optical modulators.
The present disclosure relates to optical communications equipment, and in particular to optical modulators.
BACKGROUNDIn an optical communication system, optical signals are encoded with digital streams of information and transmitted through a series of optical fiber spans towards a receiver end, where the optical signals may be decoded to retrieve or re-generate the digital streams of information in electronic domain. The encoding is typically performed by modulating the optical signals in phase, amplitude, or both. Mach-Zehnder (MZ) waveguide interferometers are often used to modulate optical signals in amplitude and/or phase.
Referring to
One drawback of the prior-art DP-QPMZ optical modulator 100 is a comparatively large size, and associated high cost. Due to their geometry, the Y-splitters 111-113 and the Y-combiners 121, 122 of the optical modulator 100 typically occupy large area on a modulator chip. A requirement to have optical taps at different locations of the optical modulator 100 may result in a further size increase of the optical modulator 100.
SUMMARYIn accordance with an aspect of the disclosure, input optical signal splitting of a planar lightwave optical modulator may be at least partially performed by one or more multimode interference (MMI) couplers, which may result in cost and size reduction. The signal combining may be optionally performed by MMI coupler(s). Output ports may be provided in the MMI couplers for optical taps. Single-mode Y-couplers may be used for further optical signal splitting and/or combining, where a precise amplitude splitting of the optical signal is required.
In accordance with the disclosure, there is further provided an optical modulator comprising:
a 1×2 multimode interference splitter having an input port for receiving light, and first and second output ports for outputting light;
first and second waveguides optically coupled to the first and second output ports, respectively;
a single-mode Y-combiner having first and second ingress ports optically coupled to the first and second waveguides, respectively, and an egress port; and
a phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide.
In accordance with an aspect of the disclosure, there is provided an optical modulator comprising:
an optical splitter comprising an input port for receiving light, first to fourth output ports for outputting light, and a multimode interference optical splitter downstream of the input port for splitting the light received at the input port;
first and second Mach-Zehnder interferometers, each comprising:
first and second waveguides each optically coupled to a different one of the first to fourth output ports;
a Mach-Zehnder combiner comprising: first and second ingress ports optically coupled to the first and second waveguides, respectively; and a first egress port; and
a phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide; and
a first optical combiner comprising: first and second inlet ports each optically coupled to a different one of the first egress ports of the Mach-Zehnder combiners of the first and second Mach-Zehnder interferometers; and a first outlet port for outputting the light modulated by the phase shifters of the first and second Mach-Zehnder interferometers.
In one exemplary embodiment, the optical splitter may further include fifth to eighth output ports for outputting light, wherein the multimode interference optical splitter is further configured for splitting at least a portion of the light received at the input port between the fifth to eighth output ports, the optical modulator further comprising:
third and fourth Mach-Zehnder interferometers, each comprising:
first and second waveguides each optically coupled to a particular one of the fifth to eighth output ports;
a Mach-Zehnder combiner comprising: first and second ingress ports optically coupled to the first and second waveguides, respectively; and a first egress port; and
a phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide; and
a second optical combiner comprising: first and second inlet ports each optically coupled to a particular one of the first egress ports of the Mach-Zehnder combiners of the third and fourth Mach-Zehnder interferometers; and a first outlet port for outputting the light modulated by the phase shifters of the third and fourth Mach-Zehnder interferometers.
In accordance with an embodiment of the disclosure, there is further provided an optical modulator comprising:
a 1×N multimode interference optical splitter comprising an input port for receiving light and first to Nth output ports for outputting light, for splitting the light received at the input port, wherein N is an integer;
first through (N/2)th Mach-Zehnder interferometers, each comprising:
first and second waveguides each optically coupled to a different one of the first to Nth output ports; and
a first phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide; and
a plurality of optical combiners, each comprising: a plurality of inlet ports each optically coupled to a different one of the first and second waveguides of the first through (N/2)th Mach-Zehnder interferometers; and a first outlet port for outputting at least a portion of the light modulated by the first phase shifters of the corresponding Mach-Zehnder interferometers.
In one exemplary embodiment, the plurality of optical combiners comprises first and second optical combiners each comprising N/2 inlet ports.
Each of the plurality of optical combiners may include a second outlet port for outputting at least a portion of the light modulated by the first phase shifters of the corresponding Mach-Zehnder interferometers. In this embodiment, the optical modulator may further include a plurality of photodetectors each coupled to a different one of the second outlet ports of the plurality of optical combiner.
Exemplary embodiments will now be described in conjunction with the drawings, in which:
While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. In
In accordance with the present disclosure, a 1×N multimode interference (MMI) splitter may be used to split an input optical signal into a required number N of portions for subsequent modulation. Various types of MMI splitters, usable in optical modulators of the present disclosure, will be considered first. Referring to
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The optical modulator 400 may further include first 461 and second 462 Mach-Zehnder interferometers, which are preferably identical to each other. Each of the Mach-Zehnder interferometer 461 and 462 may include first 421 and second 422 waveguides each optically coupled to a different one of the first 411 to fourth 414 output ports, a Mach-Zehnder combiner 406 including first 431 and second 432 ingress ports optically coupled to the first 421 and second 422 waveguides, respectively, and a first egress port 434. Each of the Mach-Zehnder interferometers 461 and 462 may further include a first phase shifter 441 operationally coupled to the first waveguide 421, and/or a second phase shifter 442 for modulating optical phase of portions of the light 365 propagating in the respective the first 421 and/or the second waveguides 422. The operation of the phase shifters 441 and 442 is similar to that of the optical modulator 300 of
The optical modulator 400 of
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First 771 and second 772 optical combiners may be provided. Similarly to the first optical combiner 471 (
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The optical splitting structures, such as the 1×2 MMI 200A of
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An optical modulator of the present disclosure may further include a 1×N MMI optical splitter or coupler, wherein N≧2, preferably N≧4. The 1×N MMI optical splitter or coupler may have an input port for receiving light, and N output ports for outputting light. The 1×8 MMI splitter 200C of
The plurality of optical combiners may include first and second optical combiners, for example the 4×1 MMI couplers 1090 of
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments and modifications, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.
Claims
1. An optical modulator comprising:
- an optical splitter comprising: an input port for receiving light, first to fourth output ports for outputting light, and a multimode interference optical splitter downstream of the input port for splitting the light received at the input port;
- first and second Mach-Zehnder interferometers, each comprising: first and second waveguides each optically coupled to a different one of the first to fourth output ports; a Mach-Zehnder combiner comprising: first and second ingress ports optically coupled to the first and second waveguides, respectively; and a first egress port; and a first phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide; and
- a first optical combiner comprising: first and second inlet ports each optically coupled to a different one of the first egress ports of the Mach-Zehnder combiners of the first and second Mach-Zehnder interferometers; and a first outlet port for outputting the light modulated by the first phase shifters of the first and second Mach-Zehnder interferometers.
2. The optical modulator of claim 1, wherein the multimode interference optical splitter is optically coupled to the input port, and comprises first and second outlet ports,
- wherein the optical splitter further comprises first and second Y-splitters each comprising an ingress port optically coupled to a different one of the first and second outlet ports of the multimode interference optical splitter,
- wherein the first Y-splitter comprises the first and second output ports of the optical splitter, and the second Y-splitter comprises the third and fourth output ports of the optical splitter.
3. The optical modulator of claim 1, wherein the multimode interference optical splitter is optically coupled to the input port, and comprises the first to fourth output ports.
4. The optical modulator of claim 3, wherein the first optical combiner comprises a multimode interference coupler comprising the first and second inlet ports, and the first outlet port.
5. The optical modulator of claim 4, wherein the multimode interference coupler further comprises a second outlet port for outputting residual light.
6. The optical modulator of claim 5, further comprising a photodetector optically coupled to the second outlet port, for detecting the residual light.
7. The optical modulator of claim 3, wherein each one of the Mach-Zehnder combiners of the first and second Mach-Zehnder interferometers comprises a multimode interference coupler comprising the first and second ingress ports, and the first egress port.
8. The optical modulator of claim 7, wherein each one of the multimode interference couplers of the Mach-Zehnder combiners of the first and second Mach-Zehnder interferometers further comprises a second egress port.
9. The optical modulator of claim 1, wherein the first and second Mach-Zehnder interferometers each further comprise a second phase shifter operationally coupled to the respective second waveguide, for modulating optical phase of light propagating in the respective second waveguide.
10. The optical modulator of claim 1, wherein the optical splitter further comprises fifth to eighth output ports for outputting light, the optical modulator further comprising:
- third and fourth Mach-Zehnder interferometers, each comprising: first and second waveguides each optically coupled to a different one of the fifth to eighth output ports; a Mach-Zehnder combiner comprising: first and second ingress ports optically coupled to the first and second waveguides, respectively; and a first egress port; and a phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide; and
- a second optical combiner comprising: first and second inlet ports each optically coupled to a different one of the first egress ports of the Mach-Zehnder combiners of the third and fourth Mach-Zehnder interferometers; and a first outlet port for outputting the light modulated by the phase shifters of the third and fourth Mach-Zehnder interferometers.
11. The optical modulator of claim 10, wherein the multimode interference optical splitter is optically coupled to the input port, and comprises first and second outlet ports,
- wherein the optical splitter further comprises first and second Y-splitters each comprising an ingress port optically coupled to a different one of the first and second outlet ports of the multimode interference optical splitter, and two egress ports;
- wherein the optical splitter further comprises third to sixth Y-splitters each comprising an ingress port optically coupled to a different one of the egress ports of the first and second Y-splitters, and two egress ports;
- wherein each one of the egress ports of the third to sixth Y-splitters is coupled to a different one of the first to eighth waveguides.
12. The optical modulator of claim 10, wherein the multimode interference optical splitter is optically coupled to the input port, and comprises the first to eighth output ports.
13. The optical modulator of claim 12, wherein each one of the Mach-Zehnder combiners of the first to fourth Mach-Zehnder interferometers comprises a multimode interference coupler comprising the first and second ingress ports thereof, and the first egress ports thereof.
14. The optical modulator of claim 13, wherein each one of the multimode interference couplers of the Mach-Zehnder combiners of the first to fourth Mach-Zehnder interferometers further comprises a second egress port for outputting residual light.
15. The optical modulator of claim 14, wherein each one of the first and second optical combiners comprises a multimode interference coupler comprising the first and second inlet ports thereof, and the first outlet ports thereof.
16. The optical modulator of claim 13, wherein each one of the first and second optical combiners comprises a multimode interference coupler comprising the first and second inlet ports thereof, and the first outlet ports thereof.
17. The optical modulator of claim 12, wherein the multimode interference optical splitter comprises a taper portion optically coupled to the input port, and an interference portion optically coupled to the first to eighth output ports.
18. The optical modulator of claim 10, wherein the multimode interference optical splitter is optically coupled to the input port, and comprises first to fourth outlet ports, the optical splitter further comprising first to fourth Mach-Zehnder multimode interference splitters each comprising an ingress port optically coupled to a different one of the first to fourth outlet ports of the multimode interference optical splitter,
- wherein the first Mach-Zehnder multimode interference splitter comprises the first and second output ports of the optical splitter;
- wherein the second Mach-Zehnder multimode interference splitter comprises the third and fourth output ports of the optical splitter;
- wherein the third Mach-Zehnder multimode interference splitter comprises the fifth and sixth output ports of the optical splitter; and
- wherein the fourth Mach-Zehnder multimode interference splitter comprises the seventh and eighth output ports of the optical splitter.
19. The optical modulator of claim 1, wherein the optical splitter and the first optical combiner are disposed on different substrates.
20. The optical modulator of claim 19, wherein the substrates of the optical splitter and the first optical combiner are selected from the group consisting of silicon, indium phosphide, and gallium arsenide.
21. The optical modulator of claim 20, wherein the first and second waveguides of each Mach-Zehnder interferometer are disposed on a substrate selected from the group consisting of lithium niobate, silicon, indium phosphide, and gallium arsenide.
22. An optical modulator comprising:
- a 1×2 multimode interference splitter having an input port for receiving light, and first and second output ports for outputting light;
- first and second waveguides optically coupled to the first and second output ports, respectively;
- a single-mode Y-combiner having first and second ingress ports optically coupled to the first and second waveguides, respectively, and an egress port; and
- a phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide.
23. The optical modulator of claim 22, wherein the 1×2 multimode interference splitter comprises a taper portion optically coupled to the input port, and an interference portion optically coupled to the first and second output ports.
24. An optical modulator comprising:
- a multimode interference optical splitter comprising an input port for receiving light and first to Nth output ports for outputting light, for splitting the light received at the input port, wherein N is an integer;
- first through (N/2)th Mach-Zehnder interferometers, each comprising: first and second waveguides each optically coupled to a different one of the first to Nth output ports; and a first phase shifter operationally coupled to the first waveguide, for modulating optical phase of light propagating in the first waveguide; and
- a plurality of optical combiners, each comprising: a plurality of inlet ports each optically coupled to a different one of the first and second waveguides of the first through (N/2)th Mach-Zehnder interferometers; and a first outlet port for outputting at least a portion of the light modulated by the first phase shifters of the corresponding Mach-Zehnder interferometers.
25. The optical modulator of claim 24, wherein the plurality of optical combiners comprises first and second optical combiners each comprising N/2 inlet ports.
26. The optical modulator of claim 24 wherein each of the plurality of optical combiners further comprises a second outlet port for outputting at least a portion of the light modulated by the first phase shifters of the corresponding Mach-Zehnder interferometers, the optical modulator further comprising a plurality of photodetectors each coupled to a different one of the second outlet ports of the plurality of optical combiners.
Type: Application
Filed: Jun 5, 2015
Publication Date: Dec 8, 2016
Patent Grant number: 9618821
Inventors: Charles M. JEWART (Enfield, CT), Yannick Lize (San Jose, CA)
Application Number: 14/732,041